488 CTENOMYS AND PETROMYS chap. 



example of 120 mm. The tail too is reduced, being in the same 

 example only 42 mm. in length. As in the last two genera the 

 large intestine is about one half of the length of the small 

 intestine. 



The " Tuco-tuco," genus Ctcnomys, has also short ears and 

 tail. The claws of the fore-feet are longer than those of the 

 hind-feet. 



A related form is Aconacmys (better known as i^cliizodon), 

 with similar external characters ; it inliabits liigh localities on 

 the Andes. 



Pcti'oriiys is the only genus of the sub-family which is not 

 American in habitat. It is an African form and there is but one 

 species. Its anatomy conforms to tliat of tlie genera already 

 considered. The main difference in structure is shown by the 

 teeth. Their surface is uneven, and differs from tliat of other 

 Hystricomorphs " in that the enamel to the inside of each upper 

 jaw - tooth and outside on each lower jaw - tooth forms two 

 tubercles, to which correspond grooves in the reverse position of 

 the applied teeth." 



Sub - Fam. 2. Loncherinae. — The genus Echinomys with 

 thirteen species belongs to the Neotropical region. The members of 

 the genus are entitled " Spiny Eats " since they have spines mixed 

 with the fur. The tail is long and the ears are very well developed. 

 Both feet are five-toed. The tail is scaly as well as haired. 

 Trichomys (also called Nclomys) is very close to the above, and is 

 also from the same part of the world. 



The genus Cannahateomys contains but one species, 0. 

 (tmhlyonyx, which was formerly included in tlie genus Bactylomys, 

 but has lately been separated by Dr. Jentink.^ Tlie animal is 

 Brazilian and has a total length of 520 mm., of wliich 320 nmi. 

 belong to the tail. It is a climbing rat, and in accordance with 

 that way of life has undergone some modifications. The fore- 

 feet are four-toed, the two middle toes Ijeing markedly longer 

 than the outer ones. The hind-feet are five-toed with the same 

 greater development of tlie two middle toes. The claws are 

 small and somewhat nail-like. 



Dactylomys, also Brazilian, and with but one species, D. 

 dactylvnus, differs from tlie last in tlie fact tliat the molars are 

 simpler in form ; they are divided into two lobes, each of wliich 

 1 Notes Lcijd. Mus. 1891, p. 105. 



